1. Field of the Invention
This invention relates to an adhesive for adhering and fixing an optical fiber to the optical connector in an optical system, and to an optical connector connected and fixed to the optical fiber by the adhesive.
2. Description of the Related Art
The general shape of an optical connector ferrule, especially a multi-fiber optical connector ferrule, is shown in FIG. 1. For example, after an optical fiber cable including four optical fibers is inserted into an optical fiber cable insert hole 5 and each of the fibers in inserted into an optical fiber insert hole 4, a thermosetting epoxy type adhesive 8 is injected into an adhesive injection opening 2. Generally, one optical fiber cable includes up to 1000 optical fibers. The adhesive 8 is hardened at about 80.degree. C. so that the optical fiber is fixed to the ferrule 1. Thereafter, the end portion of the ferrule is ground to form an optical connector. As shown, a plurality of fixing pin insert holes 3 are provided-for receiving fixing pins to connect to another optical connector. FIG. 2 is a cross sectional view taken along line II--II of FIG. 1 and wherein the adhesive 8 has been injected into the adhesive injection opening 2. The adhesive needs to have a low viscosity to fill up to the end of the optical fiber holes 4 and a high hardness to fix the optical fiber tightly when the ferrule 1 is ground.
In addition, conventionally, the thermosetting epoxy type adhesive used is selected to provide resistance to chemicals or the like. ("Optoronics" No. 3, pages 103 to 106, published in 1991)
Specifically, in the conventional adhesive, the coefficient of linear expansion is from 5.0.times.10.sup.-5 to 1.0.times.10.sup.-4, Young's Modulus is from 500 to 1000 kg/mm.sup.2, the hardening temperature is from 60.degree. C. to 100.degree. C., the filler content is from 0 weight % to 30 weight %, the viscosity at the hardening temperature is 100 cps to 1000 cps, the particle diameter of the filler is from 0.1 .mu.m to 100 .mu.m, and the rate of hardening shrinkage is 1% to 5%.
However, the conventional adhesive has had the problem(s) that the ferrule may be deformed and that the optical fiber is stressed, thereby increasing light transmission loss, by the shrinkage force of the adhesive during cooling down from the hardening temperature to room temperature, or a shrinkage after hardening.